Comment by jcelerier

> But if vec contains eg long strings, you've now murdered your perf because you're copying them out of the array instead of grabbing refs.

I've seen much more perf-murdering things being caused by

   std::map<std::string, int> my_map;
   for(const std::pair<std::string, int>& v: my_map) {
       ...
   }

than with auto though